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Home My WebLink AboutSoils Report & Observation of Excavation for Foundation Design 11.21.2017�INMAR Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado November 21, 2017 Josh Appleton 364 Glen Eagle Circle New Castle, Colorado 81647 appleton93 @ hot mail.com RECEIVED JAN 15 2018 GARFIELD COUNTY COMMUNITY DEVELOPMENT Project No.17-7-797 Subject: Subsoil Study and Excavation Observation for Foundation Design, Proposed Residence, 7625 County Road 312 (Garfield Creek Road), Garfield County, Colorado Gentlemen: As requested, H-P/Kumar performed a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated October 27, 2017. We also observed the building excavation for bearing conditions at cut depth. The data obtained from our study and recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be 2 stories with a walkout lower level and located on vacant property west of Garfield Creek Road. Ground floor will be slab -on - grade. Cut depths for the building range between about 10 feet at the uphill, south side to about 1 foot at the downhill, north side. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Subsurface Conditions: The subsurface conditions at the site were evaluated by drilling one exploratory boring near the uphill side of the excavation and logging the soils exposed in the bottom of the excavation. The log of the boring is presented on Figure 1. The subsoils encountered, below about 2 feet of topsoil, consist of mixed silty to clayey sand and gravel to a depth of 7 feet where weathered claystone/siltstone bedrock was encountered. The bedrock was slab -on -grade construction with a risk of movement. -2 - medium hard to very hard with depth. Similar soils transitioning to bedrock in the deeper cut side were observed in the building excavation at cut depth. Results of swell -consolidation testing performed on a relatively undisturbed sample of the weathered bedrock, presented on Figure 2, indicate low compressibility under existing moisture conditions and light loading and a low expansion potential when wetted. Results of a gradation analysis performed on a sample of mixed sandy clay and gravel soil (minus 3 -inch fraction) obtained from the excavation bottom are presented on Figure 3. The laboratory test results are summarized in Table 1. No free water was encountered in the boring or observed in the excavation and the soils were slightly moist. Foundation Recommendations: The soils encountered at the site are variable in type and engineering properties. The weathered bedrock tends to heave under light loading when wetted and the mixed clay, silt and gravel soils may tend to settle when wetted. Considering the subsoil conditions encountered and the nature of the proposed construction, spread footings placed on the undisturbed natural soil and bedrock designed for an allowable bearing pressure of 2,000 psf can be used for support of the proposed residence with a risk of differential movement mainly if the bearing soils are wetted. The amount of post -construction foundation settlement/heave could be 1 to 2 inches for a limited depth of wetting. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose disturbed soils and rock encountered at the foundation bearing level within the excavation should be removed or moistened and compacted. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as backfill, excluding organics and rock larger than 6 inches. Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded Generally, the movement risk is from the weathered bedrock expansion potential. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Interior non -load bearing partition walls resting on the H-P�KUMAR Project No. 17-7-797 -3 - floor slab should be provided with a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upper structure. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 -inch layer of free -draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 -inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the onsite predominantly granular soils (not weathered bedrock) devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in mountainous areas and where bedrock is shallow that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. It will be important to collect and contain water seepage outside of the building perimeter to keep water from flowing below the slab and potentially causing slab heave. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 11/ feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: H-P�KUMAR Project No. 17-7-797 -4- 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas. Free -draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. A swale should be provided where needed to direct surface runoff around the residence. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 10 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irrigation. Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory boring drilled at the uphill side of the building and to the depth shown on Figure 1, the exposed soils in the building excavation, the proposed type of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the site and there could be other variations in the subsurface conditions. If conditions encountered during construction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations may be made. H-PMKUMAR Project No. 17-7-797 -5 - This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, H -P: KUMAR Steven L. Pawlak, w. 1522 Rev by: DEHlt , Zzl a SLP/kac ` `c [IF C' Attachments: Figure 1 — Log of Exploratory Boring Figure 2 — Swell -Consolidation Test Results Figure 3 — Gradation Test Results Table 1 — Summary of Laboratory Test Results cc: Tom Oeltjenbruns (torn.tscconstruction @ztnail.cor) Kurtz and Associates — Brian Kurtz (kurtzsengineering@yahoo.corn) H-P-KUMAR Project No. 17-7-797 - 5 BORING 1 66/12 WC=8.8 DD=86 —200=43 50/2 EXCAVATION BOTTOM± LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, BROWN. SAND AND GRAVEL (SM—GM); SILTY TO CLAYEY, COBBLES, MEDIUM DENSE, SLIGHTLY MOIST, MIXED BROWN, CALCAREOUS ZONES. WEATHER SILTSTONE/CLAYSTONE; MEDIUM HARD TO HARD, SLIGHTLY MOIST, MIXED GRAY --BROWN. / SILTSTONE BEDROCK, VERY HARD, SLIGHTLY MOIST, BROWN, j WASATCH/OHIO CREEK FORMATION. 101 33/6, 50/5 I DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. WC=6.9 #10°11 DD=126 66/12 !.1 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 66 BLOWS OF A 140 POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. 150 19/6, 50/5 NOTES — 20 — 25 17-7-797 F4 f 50/3.5 H -P aClJfl AR 1. THE EXPLORATORY BORING WAS DRILLED ON NOVEMBER 13, 2017 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE EXPLORATORY BORING WAS LOCATED NEAR THE UPHILL, SOUTHEAST EXCAVATION SIDE. 3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURED AND THE LOG OF THE EXPLORATORY BORING IS PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); —200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). LOG OF EXPLORATORY BORING Fig. 1 CONSOLIDATION - SWELL SAMPLE OF: Weathered Claystone/Siltstone FROM: Boring 1 I111 10' WC = 6.9 %. OD = 126 pcf lh.etr t..t r.SLn tap* eM' bur acme,. I.AI.e. illo larUn¢ wept ,ball net b. e.pleettle t. SSW% la 1u11. without the .illt.e Opplwel at XuTe. and Aneenleise. no, Swett o.eeWtetle .lneane@p palm411 N eoreer¢. ;u. 1LS[u O -W6 �-- EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 17-7-797 1.0 APPLIED PRESSURE — KSF 10 H-PKUMAR SWELL -CONSOLIDATION TEST RESULTS 100 Fig. 2 HYDROMETER ANALYSIS SIEVE ANALYSIS 100 04 HR5 7 H15 45 WS 15 .mI+•-ap TIME READINGS 1 - ., U.S. STANDARD SERIES 0 ., . P 1 CLEAR 50UARE OPENINGS 1 1 1"-- ic MIN 1 _ ; 70 0."—MMMIZZI 1__ 30 E —�a. a..S . i" 4D �.. .. MIN M , L sohi —1��a�lwl i..— so ... _ ,_.. _..._.. 11111111111111 ®jIJ_1 30 _ .-- I� ills mi � 130 ...�..... .. I 11•1111=11= C 113 - T s0 ..—� __._.E 0 r—T 111„1 1 LI L. L1_i_ ...1 11'1 _._ ._ r ."_ ._ --TSI-.0 I AP& .017 _I .OQS .00. .014 .1357 ,073 DIAMETER .180 .500 .406 OF PARTICLES ^ 1. ■ e 4.75 IN MILLIMETERS .s It 4ee1.0 1 fa 10 .sto 711.7 127 is_ 15� o 100 200 CLAY TO SILT SAND GRAVEL FINE 1 MEDIUM 1COARSE FINE COARSE COBBLES GRAVEL 15 X SAND 24 X SILT AND CLAY 61 X LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Silty Sandy Clay with Gravel FROM: Excavation Bottom Thee. Int results apply only to the samples which were lasted, The le0lin4 report shall not be reproduced, except In full, without the written oppravol of Kumar 4 Aeeocloles, Inc. Sieve ancly.ls lasting Is performed In accordonc. with ASTII D422, ASTM C136 and/or ASTM D1140. 17-7-797 H-Pti1NMAR GRADATION TEST RESULTS Fig. 3 h-P_KUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-797 SAMPLE LOCATION NATURAL MOISTURE CONTENT °. NATURAL DRY DENSITY (ncfl _, .. GRADATION PERCENT PASSING NO. 200 SIEVE I ATTERBERG LIMITS i UNCONFINED COMPRESSIVE (PSF) __, SOIL TYPE BORING DEPTH ______._11_1_1 GRAVEL (%) _,�_.__, 1 SAND (%) j I • LIQUID PLASTIC LIMIT INDEX (%) (%) _ 1 1 j 21/2 8.8 86 43 _,_„_.. Calcareous Very Silty Sand 10 6.9 126 Weathered Claystone/Siltstone Excavation Bottom 1 5.0 15 24 61 Silty Sandy Clay with Gravel r. r